Annular filter elements are mounted in filter housings to form replaceable filter cartridges which are threadably mounted on internal combustion engines. These cartridges are known as "spin-on filters" because they are threadably mounted and removable. If a customer follows the recommended procedures for changing the filter cartridge when lubricating oil is changed, then it is unusual for the filter to clog; however, if the customer fails to change the filter cartridge, or if the lubricating oil becomes contaminated for some other reason, the filter can become clogged or otherwise blocked as to minimize flow of lubricating oil to the engine. If this happens, an engine can be destroyed or seriously damaged.
In order to avoid or at least minimize damage, filter cartridges have been configured to allow oil to bypass filter elements in the cartridges when the filter elements become clogged. The engine is thereafter supplied with at least unfiltered lubricant rather than no lubricant at all, or insufficient lubricant. It is also desirable to keep oil within the filter cartridge when the engine is not running so that when the engine is started, there is no substantial gap in the flow of lubricating oil caused by a slight delay as the filter cartridge refills with oil. This is accomplished by providing an anti-drain back valve which closes when not subjected to pressure from the engine's oil pump so as to prevent draining of oil from the filter back toward the crank case.
Millions of filter cartridges are manufactured every year and millions are disposed of. Since these filter cartridges are disposable, reduction in their cost is highly desirable. One cost reduction approach is to reduce the number of parts and to simplify assembly. Heretofore this has been difficult to accomplish without compromising the effectiveness of the filter cartridges.
In cold environments, lower temperatures of lubricating oil and mechanical components result in higher oil pump pressure and increased filter resistance to flow due to higher lubricating oil viscosity. Current oil filters do not have by-pass valves which accommodate both high operating temperatures after warm up and low temperature, cold startups which are now designed to occur at higher valve opening pressures of 11-14 psi rather than 8-11 psi. The complexity of the situation is further increased because it is desirable after warm-up, that the opening pressure of the bypass valve return to 8-11 psi.